During the first award of this proposal, the investigator has developed and clinically tested an intracavitary ultrasound hyperthermia system designed to enhance the response to radiation therapy for prostate cancer. Both the measured temperatures and the clinical follow-up supported our hypothesis that radiation effectiveness could be enhanced in this manner. In many patients, however, the measured temperatures indicated that at least part of the prostate was not adequately heated. Preliminary studies indicate that magnetic resonance imaging (MRI) offers noninvasive temperature distribution information that will allow us to utilize the full flexibility of the ultrasound arrays to control the power deposition pattern. This application proposes to test the hypothesis that the prostate target volume can be adequately heated by using MRI thermometry to obtain temperature information which in turn is used to control the ultrasound field distribution. To evaluate this hypothesis, we plan to:(1) Integrate workstation-based image analysis and control unit to the intracavitary heating system; (2) Calibrate the MRI signal during in vivo experiments in dog prostate; (3) Test and calibrate the MRI monitoring in a clinical trial; (4) Develop and optimize feedback algorithms that can be used to control the power distribution based on the image-derived temperature information; (5) Compare the feedback methods with manual control in a second clinical trial. At the end of this proposal period we will have a treatment method that will allow the complete temperature field to be monitored and controlled noninvasively. This will enable us to investigate the limits of heating technology in a clinical setting and provide the best possible temperature distribution for future clinical trials. Initially, invasive thermometry probes will be used to calibrate the MRI thermometry in every treatment but eventually completely noninvasive temperature mapping may be feasible.